How to model a window screen
As long as you aren't going to be doing any really up-close shots of the windows, just use a plane with transparency. You don't even need an image. You can procedurally generate the texture. Mix an Anisotropic BSDF shader with a Transparent BSDF shader using a Brick Texture as the mix factor. To change the size, adjust the Scale: parameter.



Result:



If the renders are looking too dark/taking too long, you can add this to the node tree: